A torsional damper comprises a hub coupled to a radial annular web; two guide washers that extend radially on either side of the annular web and are connected fixedly to one another and are movable rotationally with respect to the hub and the annular web; and elastic members and friction means mounted between the guide washers and the annular web in order to absorb and damp vibrations and rotational irregularities.
The hub is generally coupled to an input shaft of a gearbox, and a clutch disk equipped with friction linings, or a flywheel, is coupled to the guide washers.
The elastic members are most often helicoidal springs arranged circumferentially between the annular web and the guide washers. The maximum angular deflection between the web and the guide washers is reached when the spring windings are contiguous. If the torque transmitted by the torsional damper is too great, the windings experience compression, causing fatigue and premature wear on the springs.
To prevent this, the Applicant's patent application FR 2 514 446 proposes to limit the angular deflection between the web and the guide washers in both rotational directions, respectively the forward direction and the reverse direction. For this, oblong openings are provided in one of the guide washers, and pegs extend through said openings from the outer periphery of the web. Deflection is thus limited by abutment of the pegs against each of the ends of the openings.
Above a stipulated torque, and regardless of the direction of rotation, the pegs thus come into abutment against the ends of the openings and torque is transmitted directly from the guide washers to the web.
The position and length of the openings is in this case limited, however, so that the guide washers have sufficient strength. In particular, the openings must not overlap notches that serve to crimp the washers onto one another.
The angular deflection between the washers and the web allowed by such a structure is thus limited.
In the document FR 2 736 112, one of the guide washers comprises a crown having elements protruding radially inward, the outer periphery of the web having cutouts whose edges form support surfaces located on either side of the protruding elements and intended to come into abutment against them in each rotation direction.
If the cutouts are formed above the springs, the latter must be brought closer to the central hub. If the cutouts are formed not above the springs but on either side thereof, the length of the springs must necessarily be reduced. In both cases, the performance of the torsional damper is reduced.
The object of the invention is in particular to provide a simple, effective, and economical solution to these problems.